DE824635C - Process for the preparation of N-carbon anhydrides - Google Patents

Description

Process for the preparation of N-carbonic anhydrides The invention relates to focuses on the production of N-carbonic anhydrides from a-amino acids and is an improvement of the method according to patent 813 83o.

The main patent relates to a process for the preparation of N-carbonic anhydrides of α-amino acids, in which an α-amino acid containing amino hydrogen, the α-carbon of which is aliphatic in nature, i. H. is aliphatic or cycloaliphatic, or its alkali metal or alkaline earth metal or inorganic acid salt is treated with phosgene under anhydrous conditions. This process enables the production of N-carbonic anhydrides of α-amino acids in essentially one reaction step, and indeed from cheaper, more readily available materials than any process previously known to the person skilled in the art, but it has the disadvantage that low yields are obtained.

The process of the present invention is carried out in such a way that phosgene is allowed to react with an amino acid which has hydrogen on the amino nitrogen, or with its alkali metal, alkaline earth metal or inorganic acidic salts, namely the reaction takes place in an ether, which is a liquid under the reaction conditions that is chemically inert to both substances, the reactants and the end products. In order to remove the ether media more easily from the N-carbonic anhydrides formed as the end product, the use of ethers with a normal boiling point below 150 'is preferred, since the N-carbonic anhydrides are generally not heat-resistant at temperatures above 150'. The fact that the N-carbonic anhydrides are obtained with the help of a one-step reaction in higher yields with good conversions and at the same time in a state of high chemical purity from more easily accessible, cheaper chemicals, the process represents a significant technical advance, and it enables greater Measure the economic utilization of these N-carbon anhydrides for the production of new films and fibers.

The following examples, in which the data relate to parts by weight, serve to further illustrate the process according to the invention. Example I A suspension of 1 part of dl-norleucine, ie. H. dl-2-aminohexanoic acid, in 2o parts purified anhydrous yl tetrahydrofuran. The vessel was in communication with the atmosphere through drying tubes and was provided with a reflux condenser, stirrer and inlet tube connected to a container of gaseous phosgene and mounted so that its lower end was directly above the surface of the liquid. The suspension was heated to 50 to 55 ' with stirring and a measured flow of gaseous phosgene was sent into the reaction vessel until 1.5 parts (2oo0 /, the theoretical amount of phosgene required in the following equation) had been added: The clear solution thus obtained was passed through a distillation apparatus at 50 to 550 under 30 mm mercury pressure, and in this way the greater part of the tetrabydrofuran was removed. Petroleum ether was added to the concentrated tetrahydrofuran solution thus obtained, with stirring, until no further precipitation took place. The precipitate was removed by pressure filtration with nitrogen under anhydrous conditions. In this way, 1.2 parts (980 % of theory, both in terms of conversion and yield) of white crystals of the N-carbonic anhydride of dl-norleucine with a melting point of 78.0 to 78.5 'were obtained.

In order to prove the superiority of the ethereal solvents, was the above example using 20 parts of pure anhydrous benzene repeated in place of tetrahydrofuran. After treatment of the dl-norleucine-benzene-Gemisclies with phosgene under the same conditions described in the example above, only a small part of the resulting amino acid dissolved in the benzene. It was filtered the reaction mixture using nitrogen pressure under anhydrous conditions through a porous glass filter. The resulting white insoluble residue (d1-Norleticiiiliy (Irochlorid) represented gi0 /, the original amino acid. After removal of the benzene from 0.12 was obtained from the clear filtrate by distillation under reduced pressure Parts (gl> I conversion) of the N-carbonic anhydride of dl-norleucine. So that's the result Use of tetrahydrofuran (an ealer-like solvent) in place of Benzene (a colloidal hydrogen solvent) under the same reaction conditions an approximately eleven increase in the conversion into the desired clite (II-Norl (, ucine-N-carbonic anhydride.

EXAMPLE II In an apparatus similar to that described in Example I, a suspension of i-part dl-fl-phenylalanine in 20 parts of the diethyl ether of ethylene glycol was prepared and the suspension was heated to 50 to 55% with stirring. It, gaseous phosgene was introduced into the reaction vessel to 0.594 parts (theoretical Men, the ge, phosgene required) were added. The clear, colorless solution thus obtained was heated in this way (for 15 minutes to 75 '. After this time the evolution of hydrogen chloride ceased. The solution was then sent through a distillation apparatus at 60' under 20 MM mercury pressure, and in this way the larger one was removed Part of the reaction medium. Petroleum ether was then added to the concentrate obtained, with stirring, until no further precipitation took place. The precipitate was then removed by pressure filtration with nitrogen under anhydrous conditions. In this way, i, og parts (96 "/, of theory , with regard to conversion and yield) of the N-carbonic anhydride of dl-fl-Pheiiylalaiiiii in the form of white crystals with a melting point of 133.0 to 134.50.

EXAMPLE III In a reaction vessel similar to that described in Example 1 , a suspension of 29.4 parts of α-aminoisobutyric acid hydrochloride in 500 parts of purified anhydrous dioxane was rapidly stirred at from 0 to 95% , and gaseous phosgene was passed into the reaction mixture until 30.7 parts (io0.7, the theoretical amount of phosgene required) had been added. The hot reaction mixture was then forced through a suitable filter with nitrogen under anhydrous conditions. 11.9 parts (equal to 40.50 /,) de-, starting material α-aminoisobutyric acid hydrochloride remained unchanged. Approximately go0, # "of the dioxane was removed from the clear filtrate by sending it through a distillation apparatus at 6o 'under 20 mm mercury pressure Petroleum ether was then added to the clear concentrate in this way, with stirring, until no further precipitation took place. The precipitate was removed by pressure filtration with nitrogen under anhydrous conditions. In this way, 14.9 parts (54.3 (, ', Conversion and gio,', yield) of the N-carbonyl hydride of α-Ai-i-iinoisobutyric acid in the form of white crystals with an S 1 clinielzpunkt of 9_9 '.

Example IV In an apparatus similar to that described in Example I, a suspension of 10 parts 1-1, eucine in 142 parts of anhydrous diethyl ether was prepared. Gaseous phosgene was passed into the reaction vessel at room temperature for 2 hours in such a ratio that approximately twice the theoretical amount was added. The suspension was then heated in a reflux condenser for 30 minutes and the remaining solid was removed by pressure filtration with nitrogen under anhydrous conditions through a porous glass filter. In this way, 6.5 parts of 1-leucine hydrochloride (corresponding to 51.3 ",! 0 of the starting amino acid) were obtained in the form of a white crystalline solid. Removal of the diethyl ether from the clear filtrate by distillation gave 5.4 parts (450, /, conversion and 92.4 ", /, yield) of the N-carbonic anhydriol of 1-leucine in the form of white crystals with a melting point of 64 '.

Additional amino acids were converted using the procedure of this example and using diethyl ether as the medium as shown in the table below. Table I. React Conversion Yield Melting Starting position in at Punktdes tempe- N-Carbo- N-Carbo- N-Carbo- aminirlosäure ratur anhydride anhydride anhydride #C 0110 0/0 _C dl-leucine .... 34 54.5 99 47 dl-norleucine . 34 55.2 99 74 dl-isoleucine ... 34 58.4 94 79 d1-valine ..... 34 45, e, ioo 78 d1-norvaline . . 34 34.0 73 66 oll alanine ..... 34 P, 0 75 5o to 52 Example V In an apparatus similar to that described in Example, we prepared a suspension of 25 parts of α-aminoisobutyrate in 515 parts of purified anhydrous dioxane and heated the suspension to 90 to 93 ° with stirring.

At this temperature, gaseous phosgene was passed into the reaction vessel until 29 parts (approximately 10%, the theoretically required amount) had been added. Heating continued for an additional 5 minutes. -After this time, the development of hydrogen chloride stopped. The reaction mixture was then filtered hot with the aid of nitrogen pressure under anhydrous conditions through a fritted glass filter. This gave 8.4 parts (i-Amiiioisobtitter.s; itirelivdrochlorid (which corresponds to 24.5 ",;', the original Amino acid) in the form of a white crystalline solid. The greater part of the dioxane was removed from the clear filtrate by passing it through a distillation apparatus at 65 to 70 ' under 30 mm mercury pressure no further precipitation took place, the precipitate was removed by pressure filtration under anhydrous conditions to give SO 21.5 parts (680;!, conversion and go0 /, yield) white crystals of the N-carbonic anhydride of α-aminoisobutyric acid with a melting point of 94, o to 94.5 '.

The unreacted portion of the starting amino acid is in the form of his Hydrochloride recovered from the reaction mixture in the insoluble filter residue and can be converted back to the amino acid by treatment with ammonia. In this way come 920 /, the starting amino acid on N-carbonic anhydride and recovered Amino acid.

The process according to the invention, in which dioxane is used as the reaction medium, when used with various other α-amino acids gave the results shown in the table below. Table II Um- Aus wall booty Response on Used ion in N melting point Amino acid ternpe- N- Carbo- des N-Carbo- rature carbonic anhydride a, hybrid drid c 1 0/0 0/0 Ic 1-aminocyclo- hexane carboxylic acid go 57.5 96, o 104 to 105 Glycine ...... 80 43.0 43.0 100 N-methyl glycine ..... go 55 55 102 to 103 N-phenyl- glycine ..... go 76.5 76.5 136.5 to 137.0 dl-dad ..... 6obis65 65.0 65.0 77 to 78 a-amino diethvl acetic acid .. 9.5bisioo 61, o 61, o 43 N-methyl a-amino- isobutter acid hydro chloride .... 80 43.0 57.0 58 to 59 dl-fl-phenyl- alanine ..... 75 to 8o 72.5 72.5 126 to 127 N-ortho-tolyl- glycine ..... go 97.0 97.0 113 EXAMPLE VI In an apparatus similar to that described in Example I, a suspension is prepared from 10 parts of dl-methionine in 212.4 parts of dry diethyl ether. Gaseous phosgene is then passed into the reaction vessel for 40 minutes in an amount which is slightly greater than that which is absorbed. The reaction mixture is then forced through a sintered glass filter with nitrogen under anhydrous conditions. 8.5 parts of an insoluble filter residue are obtained in this way. The ethereal solvent is removed from the clear, ethereal filtrate at room temperature under reduced pressure. The thus obtained light brown 01 is ätherunlöslich when standing and developed at room temperature slowly a gas. A sample of the oil is dissolved in methylene chloride and, on standing, crystals of the N-carbonic anhydride of dl-methionine separate from the solution. This crystalline N-carbonic anhydride melts below 50 ' and decomposes rapidly at 80 to 100' with evolution of gas. Another sample of the oil slowly bubbles when exposed to the atmosphere at room temperature and melts to a clear liquid when heated gradually until gas evolution ceases. This clear, liquid melt does not develop any more gas on further heating until a temperature of 105 'is reached. At this temperature vigorous bubbling takes place and the mass becomes viscous, a sign of polymerization. EXAMPLE VII In an apparatus similar to that described in Example 1 , a suspension of 25 parts of dl-α-aminolauric acid in 17 parts of purified anhydrous dioxane is prepared and the suspension is heated to 65 'with stirring. Gaseous phosgene is then passed into the reaction vessel until 24.8 parts (approximately 2000 /, the theoretically required amount of phosgene) have been added. The clear, colorless solution thus obtained is then heated to 65 'for 15 minutes with stirring. After the solution has cooled to room temperature, it is forced through a sintered glass filter with nitrogen under anhydrous conditions. Dioxane is removed from the resulting filtrate by distillation at 63 ' under reduced pressure until the solution is concentrated to about one fifth of its volume. 453 parts of petroleum ether are then added to the concentrate obtained, with stirring. The fluffy white precipitate formed is then removed by pressure filtration with nitrogen under anhydrous conditions, dissolved in 207 parts of dioxane, treated with a part of decolorizing charcoal, filtered and reprecipitated with 453 parts of petroleum ether. After filtration in the manner described above, 22 parts (78.50% of theory) of the N-carbonic anhydride of dl-α-aminolauric acid are obtained in the form of white crystals with a melting point of 89 '. EXAMPLE VIII In an apparatus similar to that described in Example 1 , a suspension of 27 parts of dl-α-aminomyristic acid (freshly recrystallized from glacial acetic acid) in 517 parts of purified anhydrous dioxane is prepared and the suspension is heated to 65 'with stirring. Gaseous phosgene is then introduced into the reaction vessel until 45 parts (approximately 400 "/, the theoretical amount of phosgene required) have been added. The almost clear solution obtained in this way is then forced through a sintered glass filter with nitrogen under anhydrous conditions Distillation at 60 'under reduced pressure from the filtrate until the solution is concentrated to about one fifth of its original volume. 453 parts of petroleum ether are added to the concentrate obtained with stirring. The precipitate thus formed is then filtered off by pressure filtration with nitrogen under anhydrous conditions In this way, 15 parts (51.80 / (of theory) of the N-carbonic anhydride of dl-a-aminomyristic acid are obtained in the form of white crystals with a melting point of 88 to 0.16. EXAMPLE IX In an apparatus, similar that described in Example I, a suspension of 20 parts of dl-glutamic acid in 35.5 parts of purified wa is made sser-free tetrahydrofuran and heat the suspension to 55 'with stirring. Gaseous phosgene is then passed into the reaction vessel until 29.6 parts (approximately 220%, the theoretical amount of phosgene required) have been added. The almost clear solution obtained in this way is forced through a sintered glass filter with nitrogen under anhydrous conditions and the tetrahydrofuran is removed from the filtrate obtained at 60 'under reduced pressure until the solution is concentrated to about half its volume. To the obtained concentrate go6 parts Petrolätlier are added with stirring, and the thus obtained 01 isolated by decantation. Upon standing crystallized 01 lan "sam from The crude crystalline product is recrystallized three times from TetrahN-drofuran-petroleum ether mixtures UNAE during each recrystallization with decolourising charcoal treated thus obtained 5 parts (21,30 ';', of theory).. of the N-carbonic anhydride of dl-glutamic acid in the form of white crystals with a melting point of 67 to 68 '. These crystals dissolve in water with vigorous evolution of carbon dioxide. Analysis: Calculated for C "H-, NO., : N, 8.10! .. Found : _X, 8.350'o. Example X A suspension of 10 parts of i-asparagine (calculated neutral equivalent 132.1, found by perchloric acid titration 133 "5) anhydrous tetrahydrofuran purified in 222 parts is heated to 55 to 6o 'with stirring. Gaseous phosgene is then passed into the reaction vessel until 44.5 parts (about 6 poOil, the theoretical amount of phosgene required) have been added. The resulting suspension is forced through a sintered glass filter with nitrogen under anhydrous conditions. In this way 7.2 parts of the white, solid insoluble matter are removed. Most of the tetrahydrofuran is removed from the resulting filtrate by distillation at 38 to 47 minutes under reduced pressure. To the remaining brown 01 is added with vigorous stirring a small amount of petroleum ether. The 01 becomes solid and. is then dissolved in the smallest amount of tetrahydrofuran, treated with decolorizing animal charcoal and filtered. Then petroleum ether is added with stirring until the solution begins to become cloudy. The solution is then cooled in an ice bath and the precipitate formed is removed by pressure filtration with nitrogen under anhydrous conditions. After a further recrystallization from a mixture of tetrahydrofuran and petroleum ether, 1.3 parts (12.3 "of theory) of the N-carbonic anhydride of α-amino-β-cyanopropionic acid are obtained in the form of white, well-developed rosettes Product is insoluble in water, but if it remains in water for a short time, vigorous evolution of gas begins. Analysis: Calculated for C, H.N20 ,: C, 42.90 /,; H, 2, go,. ', ., H, N, 0,: (asparagine-N-carbonic anhydride) C, 38.00 /,; H, 3.80 ../ ,. Found: C, 43.5) / o; H, 3,201 .. It has thus been found that under the reaction conditions which are necessary for the formation of the N-carbonic anhydride ring from the α-aminocarboxylic acid group, the amide group is dehydrogenated to the nitrile A suspension of 9.7 parts of 1-T # TO, Sin (freshly recrystallized from water) in 413.2 parts of purified anhydrous dioxane is prepared and heated to 80 'with stirring Pour phosgene into the reaction vessel until 7.4 parts (approximately 150 " f ;, the theoretical amount of phosgene required) have been added. The almost clear, pale yellow solution obtained in this way is pressed through a sintered glass filter with nitrogen under anhydrous conditions. The dioxane is removed from the clear filtrate by distillation under reduced pressure until the solution is concentrated to about a quarter of its volume. Petroleum ether is added to the resulting concentrate with stirring until no further precipitation takes place. The precipitate is then removed by pressure filtration with nitrogen under anhydrous conditions. This gives 9.7 parts (87.40% of theory) of the N-carbonic anhydride of tyrosine, which melts at 185 to igo 'with decomposition. Analysis: Calculated for C "H" 0, N: C, 58, o0,; '0; H, 4.4) 2 / ',; N, 6.8 "/,;CO" 21.2 "/ ,. Found: C, 58, o0, /,; H, 4.70 # /,; N, 6.30 /,; CO" 20, 40j / ,. (Determined using the Knorr apparatus.) The method according to the invention is applicable to any α-aminocarboxylic acids which have at least one hydrogen atom on the nitrogen, as well as to the inorganic acidic salts of these amino acids formed by the amino group, or to the the carboxyl group formed alkali or alkaline earth metal salts of these amino acids. It is preferred to use (x-amino acids which, apart from the amino and carboxyl groups of the a-amino acid portion of the molecule, are free from groups which are reactive with phosgene under the reaction conditions, e.g. hydroxyl, thiol or other amino groups , i.e. those acids which have the amino and carboxyl groups on the one α-carbon atom as the only reactive groups, since complicated side reactions can take place with these starting materials, however, if necessary, appropriately protected derivatives of these can be used The α-aminocarboxylic acids and their inorganic acidic salts formed by the amino groups are the preferred reactants in the process, since the use of the alkali metal or alkaline earth metal salts of the α-aminocarboxylic acids formed by the carboxyl group is necessary the formation of by-products in the form of chlorides of the alkali or alkaline earth metal, whose salt verwe was found, leads. These are difficult to remove from the reaction mixture. α-Aminocarboxylic acids which, apart from the one amino and one carboxyl group, contain only carbon and hydrogen are preferred. Saturated 'ilonoaminomonocarboxyl hydrocarbons are particularly suitable because no complicated side reactions occur.

Further specific examples of α-aminocarboxylic acids, their inorganic acid salts formed by the amino group or their alkali metal or alkaline earth metal salts formed by the carboxyl group, which can be used in the process according to the invention, are the following: i-amino-x-methylcyclohexanecarboxylic acid, proline , Pipe colic acid, 3-aminotetrahydrothiophene-3-carboxylic acid, 3-Amiiiotetrahydrofuran-3-carboxylic acid, i-aminocyclopentanecarboxylic acid, N-isopropylglycine, 2-amino-4, 6, 6-trimethylöiianthsäure, valine hydrobromide, leucine hydroiodide of norleucine, the potassium salt of isoleucine, the calcium salt of fl-phenylalanine, the magnesium salt of proline, etc.

The ethers which can be used in the process according to the invention include all those which are chemically inert liquids under the reaction conditions against the reactants and against the N-carbonic anhydrides formed as end product, and the ethers can be used individually or in mixtures with one another or with other solvents such as B. chloroform, benzene, ', #ethylene chloride, toluene, or other aromatic hydrocarbons or halogenated hydrocarbons which are chemically inert to the reactants, can be used. Such ethers can be alkyl, cycloalkyl, aryl, alkyl-aryl, aryl-cycloalkyl, alkyl-cycloalkyl compounds or heterocyclic in nature and they can be substituted or unsubstituted. Any substituents should d course of functionless nature [At 1 -th in, 4th edition, Volume I, page 5-6]. H. be free of active hydrogen. Specific examples of such ethers include the following: alkyl ethers, e.g. dimethyl ether, methyl ethyl ether, methyl n-propyl ether, methyl isopropyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, diisobutyl ether; also the amyl ether, the methyl ethyl ether of ethylene glycol, the diethyl ether of ethylene glycol, methoxymethyl acetate, methoxyethyl acetate; Cycloalkyl ethers, e.g. dicyclohexyl ethers, aryl ethers, e.g. B. Diphenyl ether; Alkyl aryl ethers, e.g. B. anisole, phenetole; Aryl cycloalkyl ethers, e.g. B. phenylcyclohexyl ether; Alkyl cycloalkyl ethers, e.g. B. methylcyclohexyl ether; heterocyclic ethers, e.g. B. tetrahydropyran, 2-methyltetrahydrofuran. The reaction medium must have a larger proportion, i. H. contain more than 5o0 / "of the essential medium in order to ensure significant improvements in yield, namely free of active hydrogen, e.g. as in water, acids, amines, etc.

Since the N-Carboanhydride itself tend to decompose in the range of 150 'and higher with' considerable speeds, it is preferred to use ethers boiling below i5o0 and preferably below ioo '. In the absence of complicated side reactions, ethers are preferred which, with the exception of the etheric compounds, are essentially hydrocarbons, i.e. H. are unsubstituted, and which boil below i5o 'and preferably below ioo'. In order to avoid difficulties in removing the ethereal medium from the resulting as the end product N-Carboanhydrid, such ethers are particularly preferred, with the exception of the ether oxygen, saturated, its very nature, aliphatic, db non-aromatic hydrocarbons and their normal boiling point ioo 'or lower is. Ethers with two to four carbon atoms per ether oxygen are particularly useful because of their high dissolving power for the N-carbonic anhydride2 and their high effectiveness in the phosgene reaction.

The reaction between phosgene and the α-aminocarboxylic acids, their hydrohalogen salts or their alkali or alkaline earth metal salts in an ethereal medium can be carried out at temperatures between -5o 'and + 15o'. It is generally more convenient to carry out the reaction at the normal boiling point of the ethereal reaction medium used. When using ethers which normally boil below room temperature, it is usually preferred to carry out the reactions below atmospheric pressure and at temperatures above normal boiling point. These ethers are particularly suitable for use in the process, since they can be removed relatively easily from the N-carbonic anhydrides formed as the end product.

Depending on the reaction temperature (as in Example IV), the reactivity of the amino acid with phosgene (as in Example V) and / or the reactivity of the amino acid hydrochloride with phosgene (as in example III) Can use different amounts of the amino acid hydrochloride from the amino acid and any one of the two moles of hydrogen chloride for each mole of that formed N-carbonic anhydrides. Although the formation of amino acid hydrochloride may decrease the conversion to the desired N-carbonic anhydride are the yields still very high and in most cases almost quantitative, because what is formed in this way Amino acid hydrochloride can be isolated and directly converted into the N-carbonic anhydride can be reused, or it can optionally be converted back to the free amino acid and then reused for conversion to N-carbonic anhydride.

In general, the best one-step conversion to N-carbonic anhydride is obtained by operating at the highest temperature attainable for the specific ether medium used (most suitably at the normal boiling point of the medium or a higher temperature using one above atmospheric Pressure) and which is compatible with the heat resistance of the specific N-carbonic anhydride in question. These higher temperatures are particularly desirable when the Aminosäurehydrohalogerisalze or Al potash or alkaline earth metal of the amino acids are used as starting materials.

Phosgene is preferably used in excess, either with a slight excess, e.g. 5 to 500 / "or with a considerable, e.g. up to 5oo0 /, or higher, in order to ensure a complete reaction of the more expensive reactant, i.e. the amino acid or its derivatives, the reaction becomes so long continued until no more significant evolution of hydrogen chloride takes place.

The N-carbonic anhydrides of the α-aminocarboxylic acids are generally readily soluble in ätlierige solvents, and they will therefore be present in the liquid phase of the reaction stone, or they can otherwise by adding a suitable solvent, such as. B. chloroform, methylene chloride, benzene, etc., can be dissolved. So you only need the solid substances, i. H. to remove any starting materials that have not reacted or their hydrochloride salts by suitable methods of filtration or centrifugation, etc., and evaporate the reaction medium from the clear filtrate, preferably under reduced pressure and at temperatures below the known decomposition range of N. Carbonic anhydrides, d.Ii. below i5o 'and preferably not overioo # Jiegen. In this way, the N-carbonic anhydrides are obtained in a degree of purity which is sufficiently high for direct polymerization to film- and fiber-forming polyamides. If necessary, however, they can be prepared from a suitable solvent, such as. B, Diitli ## lätlier petroleum ether mixtures, benzene, chloroform, '\ lethylene chloride, etc., can be recrystallized. When isolating and purifying the N-carbonic anhydrides, it is important to work under anhydrous conditions in view of the known water sensitivity of these compounds.

For the preparation of the N-carbonic anhydrides of a-amino acids by reaction of the amino acids, their alkali or alkaline earth metal salts or their hydrohalogen salts with phosgene, ethereal solvents are excellent as reaction media, since they enable the preparation in high yields and good conversion of the N-carbonic anhydride directly into Facilitate a purity state high enough for the polymerization to film and fiber-forming polvineren of high molecular weight. Solvents of different types are conceivably unsuitable from one or both of these points of view. If you z. B. dl-norleucine reacts with phosgene at 50 to 55 ' in purified acetone, no crystalline N-carbonic anhydride can be isolated from the reaction mixture after removal of the acetone, in contrast to the 980 /, igen yield and conversion, which one uses obtained from tetrahydrofuran as the reaction medium for the same amino acid as indicated in Example I. If, on the other hand, β-phenylalanine is allowed to react with phosgene at 80 to 85 ' using nitromethane as the reaction medium, an essentially quantitative yield (calculated in terms of recovered, α-phenylalanine hydrochloride) of the crystalline N is obtained at 65% conversion -Carl) oanli # -drids, which, however, is light brown in color and polymerizes by itself to a polymer with a low molecular weight (as indicated in Example II), good yields and high conversions of the pure white, stable, crystalline N-carbonic anhydride of fl-phenylalanine, which under controlled conditions to a - # - phen #? lalanine pole # -meren with high Further, when the reaction of phosgene with an α-amino acid is carried out in the absence of any reaction medium, it is also reduced Obtained lower yields and conversions. Who z. If, for example, dl-norleucine is allowed to react with phosgene at 6o 'in the absence of any reaction medium, only a 21.20% conversion of the crystalline N-carbonic anhydride results in contrast to the 740% conversion and 99% yield, as indicated in the table in Example IV, with the use of dietary livestock ether as the reaction medium. The advantages of the ethereal solvents seem to be realized essentially with a-amino acids, since no crystalline N- no crystalline N- no crystalline N- Carboanlihydride can be isolated after removal of the dioxane. Small amounts of the desired product are obtained from the still used to remove the dioxane. If, on the other hand, 2, 2-dimethyl-3-aminopropionic acid is allowed to react with phosgene at 20 to 25 ' using methylene chloride as the reaction medium, a yield of 14.50% of the pure recrystallized N-carbonic anhydride is obtained.

The examples can be modified without thereby changing the framework the invention is abandoned.

Claims (2)

PATENT CLAIMS: i. Process for the preparation of N-carbonic anhydrides of a-amino acids according to patent 813 85o, characterized in that phosgene is mixed with an a-amino acid that carries hydrogen on the amino nitrogen, or with its alkali metal, Alkaline earth metal or inorganic acid salts react and the reaction performs in an ether. 2. The method according to claim i, characterized in that the reaction is carried out in an ether which, apart from the ether oxygen, contains only carbon and hydrogen atoms. 3. The method according to claim 2, characterized in that the reaction is carried out in an ether which has two to four carbon atoms per ether oxygen. 4. The method according to claim 2 or 3, characterized in that the reaction is carried out in a non-aromatic ether which, apart from the ether oxygen, contains only carbon and hydrogen atoms and has two to four carbon atoms per ether oxygen. 5. The method according to claim 4, characterized in that the reaction is carried out with an amino acid which, apart from the one amino nitrogen and the carboxylic oxygen, contains only carbon and hydrogen atoms.